Reconstitution math trips up more research labs than any other bench step. The arithmetic is simple, but the units, milligrams, millilitres, micrograms, and syringe "units", are easy to cross. This is a single worked example you can copy for any lot.
The one equation
Everything reduces to: concentration = mass ÷ volume. If you know any two, you have the third. For a research vial the mass is fixed (printed on the COA), so you choose a target concentration and solve for the diluent volume.
Worked example: a 10 mg vial
Say the lot is a 10 mg lyophilized vial and the protocol calls for a stock at 5 mg/mL. Volume = mass ÷ concentration = 10 mg ÷ 5 mg/mL = 2 mL of bacteriostatic water. Draw 2 mL, add it slowly down the vial wall, and let the cake dissolve without shaking.
Converting to a syringe marking
An insulin syringe is marked in "units," where 100 units = 1 mL. At 5 mg/mL, each mL holds 5 mg, so 1 mg sits in 0.2 mL = 20 units. If a protocol specifies a 250 µg aliquot, that is 0.25 mg × 20 units/mg = 5 units on the barrel.
Sanity-check every number
Before drawing, confirm the vial mass against the lot COA, not the label template, a multi-variant vial can carry stale label text. The authoritative mass is the figure on the Janoshik-Analytical COA archived at /lab-results/. If the two disagree, stop and verify the lot at /coa-verify/ before reconstituting.
Let the calculator do it
Our peptide reconstitution calculator takes the vial size, your target concentration, and your syringe type and returns the diluent volume and the exact unit marking, useful as an independent check on hand arithmetic. Everything Pure North ships is an HPLC-verified reference standard for laboratory research use only.